This invention relates to a retreading system including the method and apparatus for retreading tire casings with precured tread, using a flexible fluid tight member which covers the tread member. In this system of retreading, the flexible member is pressed against the tread by the fluid pressure applied to the exterior of the member so that the tread and tread casing are forced together. Simultaneously, heat is applied in order to vulcanize the rubber-based bonding medium which has been provided between the circumferential surface of the tire casing and the under-surface of the tread member.
It is conventional in this type of retreading to remove residual air from the space between the flexible member and the tread and tire casing, at one or more times during the process or continuously throughout the process. The air can be removed by connecting a conduit from the space between the flexible member and the tread member to the atmosphere or between the said space in a vacuum source. Removal of the air is accepted as an important feature of this type of retreading system because air can interfere with proper bonding of the tread to the tire casing and/or can result in deformation and/or improper seating of the tread member. It is important that the flexible member be fluid tight and be sealed to the tire casing in order to avoid leakage of pressure fluid through or past the flexible member into the space between the tread member and the tire casing. Leakage may produce the disadvantages referred to and thereby create a possibility of tire failure.
Examples of retreading systems employing the above summarized principles are described in detail in U.S. Pat. Nos. 2,966,936 (Schelkmann), 3,236,709 (Carver), 3,325,326 (Schelkmann), 3,745,084 (Schelkmann), 3,399,551 (Brodie et. al), 3,951,720 (Brodie), 4,075,047 (Brodie et. al), and 4,151,027 (Schelkman et. al). U.S. Pat. Nos. 3,325,326 and 4,151,027 disclose the concept of feeding the pressure fluid into the space between the flexible member and the assembly of the tire casing and tread so as to maintain a pressure differential between the inside and outside of the flexible fluid tight member.